badp posted an answer on this question, which was subsequently migrated to meta. It's on an SE beta, so the concept of meta users doesn't really exist, he has the same account on meta. Somehow when the question was migrated, his answer lost ownership information. I don't see how should ever occur when migrating to meta on an SE site, so I think this is a bug

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Normally we map migrated posts to a user as part of setting up user associations (implicitly part of user creations, as we try to automatically associate new users with any other accounts they have on the network).

This falls apart on meta sites because those accounts are never associated, in the traditional sense. Its a little... subtle, honestly.

Anyway, its been fixed in dev and should go out tonight sometime. I'm bringing meta sites into line with the status quo on "normal" sites, so that when a user first visits a meta site (which is when their meta account is created) they will take ownership of any posts of their's that have been migrated from the parent.